THE STIMULATORY EFFECT OF THE OCTADECANEUROPEPTIDE (ODN) ON CYTOSOLICCA2+ IN RAT ASTROCYTES IS NOT MEDIATED THROUGH CLASSICAL BENZODIAZEPINE RECEPTORS

Diazepam-binding inhibitor has been initially isolated from the rat br ain from its ability to compete with benzodiazepines for their recepto rs. We have recently shown that the octadecaneuropeptide (diazepam-bin ding inhibitor-(33-50) or ODN) induces an increase in cytosolic free C a2+ concentration ([Ca2+](i)) in astroglial cells. The purpose of the present study was to determine whether central-type benzodiazepine rec eptors or peripheral-type benzodiazepine receptors are involved in the response of cultured rat astrocytes to ODN. The mixed central-/periph eral-type benzodiazepine receptor ligand flunitrazepam (10(-10) to 10( -6) M), the specific peripheral-type benzodiazepine receptor agonist R o5-4864 (10(-10) to 10(-6) M) and the peripheral-type benzodiazepine r eceptor 'antagonist' PK 11195 (10(-9) to 10(-6) M) all induced a dose- dependent increase in [Ca2+](i). At high doses (10(-7) to 10(-5) M), t he central-type benzodiazepine receptor agonist clonazepam also mimick ed the stimulatory effect of ODN on [Ca2+](i). However, the [Ca2+](i) rise induced by ODN was blocked neither by PK 11195 nor by the central -tppe benzodiazepine receptor antagonist flumazenil (10(-6) M each). B inding of [H-3]flunitrazepam to intact astrocytes was displaced by low concentrations of the peripheral-type benzodiazepine receptor ligands flunitrazepam, Ro5-4864 and PK 11195, and by high concentrations of c lonazepam. In contrast, ODN did not compete for [H-3]flunitrazepam bin ding in intact cells. These data indicate that the effect of ODN on Ca 2+ mobilization in rat astrocytes is mediated by high affinity recepto rs which are not related to classical benzodiazepine receptors. (C) 19 97 Elsevier Science B.V.